Read every setting through viper and rename the settings (closes #211)

Every setting of discriminator and rproxy is read through viper, in place
of the os.LookupEnv function Main passed down. NewViper turns AutomaticEnv
and AllowEmptyEnv on, so a setting that is set but empty reads as set. A
setting may also be given as a file, the _FILE form, which rproxy's
settings now have too; rproxy still writes nothing to disk.

The settings are renamed. Discriminator's take the prefix SWW_WAF_,
rproxy's take SWW_RPROXY_, and the shared SWW_COMMAND keeps SWW_. The Core
Rule Set's settings take SWW_WAF_CORE_RULE_SET_ rather than SWW_WAF_WAF_.
Every place a name appeared changed: the code, the viper keys, tests,
documents, examples, the README's settings table and the image files.

Model: deepseek-v4-pro

internal/discriminator/rulefiles_test.go

@@ -34,14 +34,14 @@ func TestEachRuleAction(t *testing.T) {
 	line := s.get(client, http.StatusOK, requestlog.ActionForward)
 	wantRuleIDs(t, line, "noted")
 
-	// A block rule refuses with 403, whatever SWW_BAN_RESPONSE is, and
+	// A block rule refuses with 403, whatever SWW_WAF_BAN_RESPONSE is, and
 	// bans no one.
 	line = s.request(client, "/blocked", http.StatusForbidden,
 		requestlog.ActionRuleBlocked)
 	wantRuleIDs(t, line, "noted", "blocked")
 	s.get(client, http.StatusOK, requestlog.ActionForward)
 
-	// A ban rule refuses with SWW_BAN_RESPONSE, and bans the client for
+	// A ban rule refuses with SWW_WAF_BAN_RESPONSE, and bans the client for
 	// seven days, the default.
 	line = s.request(client, "/.env", http.StatusTooManyRequests, requestlog.ActionBanned)
 	wantRuleIDs(t, line, "noted", "probe")
@@ -101,7 +101,7 @@ func TestNextClearSignOfAttackAfterABanBansPermanently(t *testing.T) {
 		attackBanDuration: "1h",
 	})
 
-	// The first probe bans for SWW_ATTACK_BAN_DURATION.
+	// The first probe bans for SWW_WAF_ATTACK_BAN_DURATION.
 	line := s.request(client, "/.env", http.StatusForbidden, requestlog.ActionBanned)
 	if line.BanExpires != requestlog.FormatTime(clk.Now().Add(time.Hour)) {
 		t.Errorf("log line has ban_expires %q, want an hour on", line.BanExpires)
@@ -122,8 +122,8 @@ func TestRulesComeAfterTheOtherChecks(t *testing.T) {
 	t.Parallel()
 
 	const (
-		allowed = "192.0.2.60" // in SWW_ALLOW_NETS
-		exempt  = "192.0.2.50" // in SWW_RATE_LIMIT_EXEMPT_NETS
+		allowed = "192.0.2.60" // in SWW_WAF_ALLOW_NETS
+		exempt  = "192.0.2.50" // in SWW_WAF_RATE_LIMIT_EXEMPT_NETS
 	)
 
 	s, _, server := startWithClock(t, "", map[string]string{
@@ -133,7 +133,7 @@ func TestRulesComeAfterTheOtherChecks(t *testing.T) {
 		rateLimitPerMinute:  "1",
 	})
 
-	// A client in SWW_ALLOW_NETS is not checked.
+	// A client in SWW_WAF_ALLOW_NETS is not checked.
 	line := s.request(allowed, "/.env", http.StatusOK, requestlog.ActionForward)
 	wantRuleIDs(t, line)